Why the study?
Do high- and low-molecular-weight heparins affect thrombin-thrombomodulin interaction and protein C activation?
Do high- and low-molecular-weight heparins affect thrombin-thrombomodulin interaction and protein C activation?
Heparin at therapeutic concentrations reduces the affinity of thrombin for thrombomodulin and the rate of protein C activation, with the effect proportional to heparin's molecular mass.
May impair protein C activation in experimental models; leaves open clinical relevance of heparin molecular mass effects.
BACKGROUND: Thrombin-thrombomodulin (TM) interaction, which is critical for accelerating the protein C anticoagulant pathway, involves the heparin-like domain of TM. This study was aimed at investigating the possible effect of heparin on thrombin-TM binding and protein C activation. METHODS AND RESULTS: The affinity of thrombin-TM interaction was studied by a functional method, based on the ability of thrombin-TM adduct to activate protein C, and by evaluation of the binding of thrombin to immobilized TM. Both experimental approaches showed that the affinity of thrombin-TM interaction was decreased by micromolar heparin concentrations. Heparin had no significant effect when a recombinant TM form, lacking the chondroitin sulfate moiety, was used. Furthermore, it was also shown that the inhibitory effect of heparin was directly proportional to the heparin molecular mass (molecular weight range, 3 to 16 kDa), which suggests that the effect was mediated by formation of electrostatic bonds between heparin and thrombin. CONCLUSIONS: These results indicate that heparin at therapeutic concentrations reduces the affinity of thrombin for TM and the rate of protein C activation. The magnitude of this effect is proportionally linked to the molecular mass of heparin.
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Cristofaro et al. (1998) studied this question.
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